Due to the evolution of information technology, the amount of information available to people has become vast. The information explosion means that the number of items in only one information category, such as music, movies, books, news, web pages, has become so large that a single person cannot possibly view them all in order to select the relevant ones. For example, the list of music service providers in the Internet is growing, as well as downloadable music and videos.
In order to help their customer's find interesting items, many commercial sites on the Internet provide their users with recommendations. Typically these recommendations are generated on the basis of the user's preference information, records of the purchased item(s) and the utilization of collaborative filtering. The service provider on the commercial site receives the user's preference information when the users explicitly rate, for example, music or books that they like. In collaborative filtering, the users' ratings are aggregated and when a user rates or buys something, the collaborative filter on the commercial site checks for other people who liked or bought the same item and what other items those people also liked or bought and then returns these items as recommendations to the user. One problem with these explicit ratings is that users seldom change ratings because it is laborious and therefore the explicit ratings are static profiles not reflecting the current, relevant likes and dislikes of the user—even when the ratings are updated by the commercial site every time the user buys something. Another problem is that the user has to perform the rating separately for each commercial site he uses.
A certain kind of “automatic rating feature”, called tracking, is provided by presentation applications, such as Microsoft's Media Player or Apple's iTunes, running in computers for playing music and video. The presentation applications typically keep track of when you last played a song, what year the song was released, how many times each song has been played, when it was imported to the song library, etc. One of the problems associated with the above arrangement is that tracking is tied to a particular presentation application (i.e. Media Player or iTunes), each of which stores the tracked information in a proprietary format, and if a user changes the presentation application, the previously tracked information cannot be used by the new application. Another problem is that the tracking is tied to the corresponding personal computer that tracks the music played by the computer. However, music is more and more often listened from a portable digital player, which can be synchronized with the computer's music library. The portable players do not track played music.